This invention relates to a toner for developing an electrostatic image and an image forming method applicable in a copy machine or a printer.
Currently, a technology for synthesizing a toner for developing an electrostatic image by a polymerization process has been known. However, the toner particle synthesized by a suspension polymerization method has a shortcoming that such the particle is inferior in the cleaning ability since it has a spherical shape.
Consequently, a method by which a resin particle prepared by a method such as a emulsifying polymerization method and a colorant particle are associated, by coagulation or fusion, is utilized for obtaining a toner particle having an irregular, non spherical, shape.
On the other hand, a heating roller fixing method by which an image forming support carrying thereon a toner image is passed between a heating roller and a pressure roller is utilized for fixing a toner image formed on the image forming support such as a paper sheet.
However, the heat roller fixing method has a shortcoming that a stain tends to be formed by an off-set phenomenon caused by adhesion of the fused toner onto the heating roller.
Then it has been known that silicone oil is coated on the surface of the heating roller of the fixing device for giving a toner releasing ability to the heating roller as a means for inhibiting the off-set phenomenon. Such the method is advantageous at a point that the kind of toner is not limited.
In such the method, however, the stain is become formed in the course of application for a long period since the silicone oil supplied for the long period on the surface of the heating roller is modified, gelled, and the releasing ability of the heating ability is reduced accompanied with the passing of the time. As a result, the life time of the fixing device is made shorter compared to the case in which no silicone oil is coated. Moreover, a volatile component contained in the silicone oil is volatilized by heat of the heating roller surface and adhered onto an optical system or an electrode of the apparatus, as a result of that a fault of the image is occurred.
From the viewpoint as above-mentioned, it is required to eliminate or extremely reduce the amount of the silicone oil to be supplied to the fixing device, heating roller.
Corresponding to such the requirement, it is widely applied to giving the releasing ability to the toner itself by addition of a releasing agent to the toner.
As the method for adding the releasing agent to the polymerized toner obtained by the polymerization method, a method by which the resin particle and a particle of the releasing agent is associated.
By such the method, however, the sufficient amount of the releasing agent cannot be introduced into the associated particle or colored particle. Furthermore, the contents of the releasing agent in the individual formed particles are different from each other. As a result, sufficient releasing property or anti-offset property of the whole toner cannot be realized.
Moreover, in the case of a developer comprising the associated particle composed of the resin particle and the releasing agent particle, the releasing agent is released from the associated particle and the released releasing agent causes degradation of the developer or gives a bad influence to the photoreceptor by adhering thereon.
As above-mentioned, any means to satisfy the anti-offset ability or releasing ability when no or extremely small amount of the releasing agent is supplied, has not be found yet.
On the other hand, it is necessary to raise the temperature and pressure of the fixing for increasing the fixing ability, or the adhesiveness of the toner to the image forming support. The offset tends to be occurred under both of such the conditions. Accordingly, many means for improving the anti-offset ability by selection of the resin from the viewpoint of the viscosity of the toner in the fused state have been proposed. It is extreme important problem in the fixing process that a fixable temperature range, or the range between the lowest fixing temperatures at which the fixing is can be carried out and the temperature at which the offset is occurred, can be made how wider. Such the problem is not sufficiently solved particularly when a small particle toner or a colored toner is used.
Moreover, there are a requirement to improve the initial image quality and problems such as the prevention of the degradation in the image quality and the fine line reproducibility accompanied with a repeating use of the toner. For example, it is necessary to solve the problems of lowering of the gradation and the fine line reproducibility, variation of the image density, unevenness of the density and fogging. Important causes of such the problems include difficulty and instability of the charging amount control of the toner. The controlling and stabilizing of the charging amount are considerably difficult since the triboelectricity is utilized for charging. Many means using a specific binder of toner, a charge controlling agent, an external additive or another additive have been proposed. However, a higher image quality and a higher durability of developer are further required accompanied with the raising in the performance and the reliability of each of the image forming processes.
Recently, the electrophotography is applied in various fields. For example, the electrophotography is used for not only a monochromatic copying machine but also for a printer to be used as an output terminal of computer, a color copying machine and a color printer. Accompanied with progress of such the applications, the requirement for the image quality is made higher. Particularly, in a multicolor image forming method in which a multicolor image is formed by plural toner images each composed of a color toner are piled up, a variation of the secondary color formed by the color pilling up is made larger by the small variation of the developing ability, or the amount of the toner, caused by a slight variation in the electro conductivity and a variation the transferring property of the halftone image. Consequently, the stabilization of the electro conductivity is strongly required. Moreover, the rising in the fine line reproducibility and the stability of the electro conductivity are also strongly required in an image formed by a digital exposure method.
It has been known as a technology to raise the fixing ability of a toner to make a micro domain by a crystalline substance such as crystalline polyester and an amorphous high molecular substance. Japanese Patent Publication Open to Public Inspection Nos. 63-27855 and 63-27856 each describes a toner containing a polymer prepared by chemically drafting or blocking amorphous vinyl polymer and crystalline polyester as a resin component. It is difficult, however, to lower the viscosity of the fused resin by the use of the crystalline polyester even when such the technology is applied, and there is a limitation on the raising of the fixing ability. For raising the fixing ability of the toner, the crystalline polyester must be existed uniformly in a certain ratio and maintaining some degree of the domain structure in the toner particle. However, any method to exist the crystalline polyester in such the status, the domain structure, is not known. Accordingly, the fixing ability can hardly be raised by introducing the crystalline polyester.
The first object of the invention is to provide a toner for developing an electrostatic image, which is excellent in the anti-offset ability and is able to give a high quality image without stain for a long period of time.
The second object of the invention is to provide a toner for developing an electrostatic image, which releases no substance to be adhered onto the photoreceptor.
The third object of the invention is to provide a toner for developing an electrostatic image, which is able to form an image without any stain and fault for a long period of time even when he toner is used in an image forming method including a process for forming a fixed image by a fixing device to which no or extreme small amount of silicone oil is supplied.
The fourth object of the invention is to provide a toner for developing an electrostatic image having a high fixing ability.
The fifth object of the invention is to provide a toner for developing an electrostatic image which is excellent in the developing ability and the fine line reproducibility and is able to form a high quality image for a long period of time.
The sixth object of the invention is to provide an image forming method using an excellent toner as above-mentioned.
The invention and its preferable embodiments are described.
1. A toner for developing an electrostatic image comprising a resin, a colorant and a releasing agent, wherein the toner particles are obtained by salting out/fusion-adhering a resin particle comprising a binding resin and a releasing agent together with a colorant particle, and the toner comprises the toner particles having a variation coefficient of not more than 16% and a number variation coefficient of the number particle size distribution of not more than 27%.
2. The toner of item 1 wherein the toner particles not less than 65% in number has a shape coefficient of from 1.0 to 1.6.
3. The toner of item 1 wherein the toner particles not less than 65% in number has a shape coefficient of from 1.2 to 1.6.
4. The toner of item 1 wherein the toner particles not less than 50% in number are particles having no corner.
5. The toner of item 1 wherein a number average particle size of the toner particles is from 3 to 8 xcexcm.
6. The toner of item 1 wherein a sum M of at least 70 percent, sum M is obtained by adding relative frequency m1 of toner particles, included in the most frequent class, to relative frequency m2 of toner particles included in the second frequent class in a histogram showing the particle size distribution, which is drawn in such a manner that natural logarithm lnD is used as an abscissa, wherein D (in xcexcm) represents the particle size of a toner particle, while being divided into a plurality of classes at intervals of 0.23, and the number of particles is used as an ordinate.
7. The toner of item 2 wherein the toner particles not less than 50% in number are particles having no corner and a number average particle size of the toner particles is from 3 to 8 xcexcm.
8. The toner of item 1 wherein the releasing agent is represented by the Formula (1),
R1xe2x80x94(OCOxe2x80x94R2)nxe2x80x83xe2x80x83(1):
wherein R1 and R2 each represent a hydrocarbon group having from 1 to 40 carbon atoms, which may have a substituent, and n is an integer of 1 to 4.
9. The toner of item 8 wherein R1 represent a hydrocarbon group having from 1 to 20 carbon atoms, and R2 represent a hydrocarbon group having from 16 to 30 carbon atoms and n is an integer of from 2 to 4.
10. The toner of item 1 wherein content ratio of the releasing agents in the toner is from 1 to 30 percent by weight.
11. The toner of item 1 wherein melting point of the crystalline polyester is from 50 to 130xc2x0 C.
12. The toner of item 1 wherein number average molecular weight of crystalline polyester is from 1,500 to 15,000, and melt viscosity of a crystalline polyester (viscosity at melting point plus 20 degrees) is not more than 100 dPaxc2x7s.
13. The toner of item 1 wherein a containing ratio of crystalline polyester in the toner is 1-50 weight parts.
14. The toner of item 7 wherein the releasing agent is represented by the Formula (1),
R1xe2x80x94(OCOxe2x80x94R2)nxe2x80x83xe2x80x83(1):
wherein R1 and R2 each represent a hydrocarbon group having from 1 to 40 carbon atoms, which may have a substituent, and n is an integer of 1 to 4, melting point of the crystalline polyester is from 50 to 130xc2x0 C., and number average molecular weight of crystalline polyester is from 1,500 to 15,000, and melt viscosity of a crystalline polyester (viscosity at melting point plus 20 degrees) is not more than 100 dPaxc2x7s.
15. A toner for developing an electrostatic image comprising a resin, a colorant and a releasing agent, wherein the toner particles are obtained by salting out/fusion-adhering a resin particle comprising a binding resin and a releasing agent together with a colorant particle, and the toner comprises the toner particles having no corner of not less than 50% in number, and a number variation coefficient of the number particle size distribution of not more than 27%.
16. The toner of item 7 wherein the toner particles not less than 65% in number has a shape coefficient of from 1.0 to 1.6.
17. The toner of item 8 wherein the toner particles not less than 65% in number has a shape coefficient of from 1.2 to 1.6.
18. The toner of item 10 wherein the toner particles not less than 50% in number are particles having no corner and a number average particle size of the toner particles is from 3 to 8 xcexcm.
19. The toner of item 8 wherein a sum M of at least 70 percent, sum M is obtained by adding relative frequency m1 of toner particles, included in the most frequent class, to relative frequency m2 of toner particles included in the second frequent class in a histogram showing the particle size distribution, which is drawn in such a manner that natural logarithm lnD is used as an abscissa, wherein D (in xcexcm) represents the particle size of a toner particle, while being divided into a plurality of classes at intervals of 0.23, and the number of particles is used as an ordinate. 20. The toner of item 15 wherein the releasing agent is represented by the Formula (1),
R1xe2x80x94(OCOxe2x80x94R2)nxe2x80x83xe2x80x83(1):
wherein R1 and R2 each represent a hydrocarbon group having from 1 to 40 carbon atoms, which may have a substituent, and n is an integer of 1 to 4, melting point of the crystalline polyester is from 50 to 130xc2x0 C., and number average molecular weight of crystalline polyester is from 1,500 to 15,000, and melt viscosity of a crystalline polyester (viscosity at melting point plus 20 degrees) is not more than 100 dPaxc2x7s.
21. A toner for developing an electrostatic image comprising a resin, a colorant and a releasing agent, wherein the toner particles are obtained by salting out/fusion-adhering a resin particle comprising a binding resin and a releasing agent together with a colorant particle, and the toner particles not less than 65% in number has a shape coefficient of from 1.2 to 1.6, and a variation coefficient of the toner particles is not more than 16%.
22. The toner of item 21 wherein the toner particles not less than 50% in number are particles having no corner.
23. The toner of item 21 wherein a sum M of at least 70 percent, sum M is obtained by adding relative frequency m1 of toner particles, included in the most frequent class, to relative frequency m2 of toner particles included in the second frequent class in a histogram showing the particle size distribution, which is drawn in such a manner that natural logarithm lnD is used as an abscissa, wherein D (in xcfx81m) represents the particle size of a toner particle, while being divided into a plurality of classes at intervals of 0.23, and the number of particles is used as an ordinate.
24. The toner of item 21 wherein the releasing agent is represented by the Formula (1),
R1xe2x80x94(OCOxe2x80x94R2)nxe2x80x83xe2x80x83(1):
wherein R1 and R2 each represent a hydrocarbon group having from 1 to 40 carbon atoms, which may have a substituent, and n is an integer of 1 to 4, melting point of the crystalline polyester is from 50 to 130xc2x0 C., and number average molecular weight of crystalline polyester is from 1,500 to 15,000, and melt viscosity of a crystalline polyester (viscosity at melting point plus 20 degrees) is not more than 100 dPaxc2x7s.